1. Field of the Invention
The present invention relates to a method of clay stabilization in oil reservoirs that are subject to anionic or caustic chemical flooding via enhanced oil recovery techniques, and particularly, to the introduction of a cationic organic polymer having clay stabilization properties into an oil reservoir treatment area followed by introduction of a non-anionic aqueous spacer fluid in an amount sufficient to reorient the polymer in a monomolecular layer prior to injection of the anionic or caustic chemical flood.
2. Description of the Prior Art
Cationic organic polymers have become widely used in preventing permeability damage due to clay swelling and disintegration in subterranean formations during oil and gas production. However, these cationic organic polymers form precipitates when they contact anionic chemicals such as petroleum sulfonates, partially hydrolyzed polyacrylamides, and certain microbial polysaccharides used in enhanced oil recovery. In the past, the solution to this problem has been either the use of a mutual solvent system or employment of nonionic surfactants and unhydrolyzed polyacrylamides or nonionic polysaccharides. This results in higher costs and/or reduced oil recovery.
A similar problem is encountered when caustic flooding is used as an enhanced oil recovery process. The oil reservoirs considered as caustic flood candidates are normally shallow and have quite high clay contents. The injected fluids: a conditioning fluid to reduce the salinity of formation water, especially the concentration of divalent metal cations, and a high pH solution (usually a sodium hydroxide, sodium silicate, or sodium carbonate solution) are of low salinity and can easily cause clay swelling and migration of fine particles leading to reduced formation permeability. The cationic organic polymer clay stabilizers that have been developed and are widely used to help control clay swelling and fine particle migration undergo a bimolecular elimination or other decomposition reactions in the high pH environment caused by caustic flooding. This bimolecular elimination reaction converts cationic nitrogen atoms to amines (see Equation 1 below) and can also substantially reduce the molecular weight of the clay stabilizer when the cationic atom is part of the polymer backbone (see Equation 2 below).